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'Squeezed' Light Can Give Nano-Imaging a Much-Needed Boost

It's one thing to produce nano-scale materials, but it's an entirely different thing imaging them.

Nanomaterials have many applications, especially in electronics, but they have one issue: They are so small that they don’t reflect enough light to show fine details, such as colors, even with the aid of the most powerful microscopes. 

Now, researchers from UC Riverside may have come up with a solution. They have conceived of an imaging technology that compresses lamp light into a nanometer-sized spot, holding that light at the end of a silver nanowire. This allows it to reveal previously invisible details such as colors. 

The technique is not entirely new. It has been used in previous experiments to observe the vibration of molecular bonds at 1-nanometer spatial resolution without the need for a focusing lens.

The researchers then modified the tool to measure signals spanning the whole visible wavelength range, essentially squeezing the light from a tungsten lamp into a silver nanowire with near-zero scattering or reflection.

“It is like using your thumb to control the water spray from a hose,” Ming Liu, associate professor in UC Riverside’s Marlan and Rosemary Bourns College of Engineering and study co-author, said.

“You know how to get the desired spraying pattern by changing the thumb position, and likewise, in the experiment, we read the light pattern to retrieve the details of the object blocking the 5 nm-sized light nozzle.” 

The light is then focused into a spectrometer where it scans the probe over an area, recording two spectra for each pixel. The carbon nanotubes then can exhibit their colors.

“The atomically smooth sharp-tip silver nanowire and its nearly scatterless optical coupling and focusing is critical for the imaging,” Ruoxue Yan, study co-author, said. “Otherwise there would be intense stray light in the background that ruins the whole effort."

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The new study is published in Nature Communications.

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